Impl Block

Not to be confused with Impl Trait

blocks declare type-associated items.

= Inherent  =

An  block may be simply associated with a type. This is called an "inherent impl", and has the syntax.

An inherent  must be declared in the same crate as the type itself.

= Trait  =

See also Traits.

A trait  declares all associated items that are required by the trait definition, and look like. Trait s are subject to the Orphan Rules.

= Associated Items =

Associated Functions
Associated functions are the foundation of "object oriented programming" in Rust. They provide a standard, easy-to-understand way to associate data types with functions that operate on them.

An associated function may or may not accept a  parameter. If it does, that function is usually called a "method." Methods support method call syntax, which eliminates the need to explicitly specify the type name that the method is associated with, using  syntax:

DataType::Method MessageType::None DataType::Method MessageType::None

The first two method calls,  and , were statically dispatched to the corresponding impl blocks and functions based on the type of the receiver.

If the type seems ambiguous, then it can still be specified by hand. This is known as fully-qualified function call syntax.

Associated Types and Constants
Other associated items have no support for the  parameter, and typically need to be explicitly named on the type, just like if they had been declared directly inside a module.

Additionally, associated types must be type aliases. This, for example, is not allowed: